Borehole televiewer system depth monitoring and recording system

ABSTRACT

A method and an apparatus for recording the depth of a well logging apparatus is provided. The method and apparatus include the direct acquisition of broad depth information from the logging system conversion of the broad depth information to an acceptable digital signal and recording that signal on the audio track of a video cassette recorder. A microcontroller is used to convert broad depth information from either the logging system or the video cassette recorder (in the playback mode) to actual depth and depth rate for use by other displays and plotters.

This application is a continuation of application Ser. No. 07/574,425,now abandoned, filed Aug. 28, 1990.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is cross-related to U.S. patent application Ser. No.07/574,315 entitled a "Borehole Televiewer Analog Interface For VideoCassette Recorders" (now abandoned) and U.S. patent application Ser. No.07/966,129 which is a continuation of Ser. No. 07/819,912 (nowabandoned) which is a continuation of U.S. Pat. No. 5,099,236 whichissued Mar. 24, 1992.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to well logging apparatus and more particularlythe monitoring of depth information for well-logging operations.

2. Description of the Related Art

Zemanek, U.S. Pat. No. 3,369,626 discloses an ultrasonic tool for use inscanning the inner surface of an open well or of casing in a borehole.The tool, which is commercially known as the "borehole televiewer"creates a high resolution picture of the inner surface underinvestigation. The borehole televiewer is used to "see" the innersurface under investigation through drilling mud or other boreholefluids. In an open borehole, the borehole televiewer provides a pictureof the formations surrounding the borehole. In a cased borehole, theborehole televiewer provides a picture of the inner surface of thecasing, which can be used to determine the condition of the innersurface.

The borehole televiewer uses a rotating ultrasonic transducer, thetransducer has a transmitter, to generate acoustic waveforms, and areceiver, to receive the acoustic return. The acoustic return is causedby the reflection of the generated acoustic waveform from the innersurface under investigation.

The acoustic return has two measured parameters, the time of travel ofthe acoustic return and the amplitude, which give an indication of thecondition of the investigated surface.

The transducer rotates three revolutions per second, is pulsed about 500times per revolution and is pulled up the borehole at a speed of about 5feet per minute. The transducer spot size, the rotational speed, thepulse repetition rate and the vertical speed combined to provide fullcoverage of the investigated inner surface, resulting in high aerealresolution of the inner surface. In the past, depth was correlated withteleviewer information by a voice entry on an audio track of a videocassette recorder (VCR). Depth was constantly monitored by the operatorand verbally entered every five feet. This type of operation, however,is very tedious for an operator because the boreholes underinvestigation tend to be very deep and the logging rate is very low. Theoperator fatigue inherent in this evolution results in human errorsbeing made in the depth correlations.

There is a need, therefore, for a simple and accurate boreholeteleviewer depth monitoring and recording system which can relieve theoperator of this time consuming and tedious task. In addition, there isalso a need for a depth monitoring and recording system which providesprecise logging rate information at slow logging speeds.

SUMMARY OF THE INVENTION

The present invention will eliminate operator tedium and human error indepth correlations and simply provide an accurate borehole televiewerdepth.

The present invention also includes a depth monitoring and recordingsystem for a borehole televiewer comprising an encoder interface, amicrocontroller electrically connected to the encoder interface and areoording device electrically connected to the microcontroller.

Another useful embodiment of the method of the present inventionincludes the recording of depth information in synchronicity withteleviewer data from a borehole televiewer system comprising providing adata input signal having a synchronizing pulse and a depth signal havingthe same synchronizing pulse and recording the depth and the acousticreturn signals on two separate channels.

In addition to solving the problems stated above, the present inventionhas additional advantages. A major advantage of this invention isrelieving the operator of the time consuming and tedious task ofverbally entering the depth on VCR audio channel. Additionally, thedepths are monitored more accurately and are available in the televiewerunit. Furthermore, the logging depth is monitored more precisely than aconventional logging units which are not normally concerned with loggingrates as slow as 5 feet per minute. The present invention also has theadditional advantage that its encoding scheme is simple combinatoriallogic and the decoding scheme uses very simple analog and logiccomponents. The present invention also has the advantage of reducing thenumber of recording channels necessary for televiewer operationsupporting information and thereby allowing continued use of otheranalog channels for voice entry.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of the present invention will become apparent when reference ismade to the following description taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a simplified block diagram of a well logging system.

FIG. 2 is a simplified block diagram of a depth monitoring and recordingsystem for a well logging system.

FIG. 3 shows the time relationship for a quadrature pulsing systemsignals for up and down counts.

FIG. 4 shows an example of an depth signal interface for a quadraturepulsing system.

FIG. 5 shows the timing relationship for an embodiment ofan encodeddepth signal.

FIG. 6 shows a block diagram for depth decoding for use in a playbackcircuit of a VCR.

FIG. 7 shows an input signal for a borehole televiewer and acorresponding Automatic Gain Control (AGC) adjusting signal.

FIG. 8(a) shows the time relationship of a received synchronizing pulseand acoustic return signal.

FIG. 8(b) shows the time relationship of a modified synchronizing signalwith a superimposed AGC control signal and a modified acoustic returnsignal.

FIG. 8(c) the time relationship shows the synchronizing signal of FIG.9(b) and the modified acoustic return signal of FIG. 8(b) transformedinto a time of travel and an amplitude signal.

FIG. 9 shows a bipolar version of the signal in FIG. 8(c) with itsassociate AGC control pulse.

FIG. 10 shows the bipolar signal of FIG. 9 along with an added expandedacoustic pulse embodiment.

FIG. 11 shows the signal of FIG. 10 along with a vertical synchronizingsignal.

DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 is a simplified block diagram of a well logging system. There isalso shown a schematic longitudinal cross section of a cased wellborehole 12, an ultrasonic logging apparatus 14 and support surfaceequipment 16 with which the present invention can be practiced.

The well borehole 12, which is drilled into the earth 18, is forproducing oil or natural gas. The well borehole 12 is lined with alength of casing 20. The casing wall has inner and outer surfaces 22,24. Cement 26 fills the annulus between the casing 20 and the walls ofthe borehole 12, for at least some of the length of the casing. Cement26 is used primarily to isolate one formation from another. The interiorof the casing is filled with borehole fluids 28, which may be drillingmud, oil or both.

The ultrasonic logging apparatus 14 is located within casing 20 andmoves up or down the borehole for logging operations. The loggingapparatus 14 is suspended inside of the casing by a logging cable 30,which provides electrical power and communication channels from thesurface equipment 16. The ultrasonic logging apparatus 14 includes anultrasonic transducer (not shown) which serves as a transmitter andreceiver. Transducer is oriented so as to generate acoustic waveformsnormal to the walls of the casing 20. The acoustic transducer has aresonant frequency of about 20 megahertz and a bandwidth of about1.0-2.5 megahertz. The logging apparatus is kept centered along thealong the longitudinal axis of the casing 20 by centralizers (notshown).

The ultrasonic logging apparatus 14 transmits data uphole to the surfaceequipment 16 over logging cable 30. The surface equipment 16 includes asheave wheel 32 over which the logging cable 30 passes. An opticalencoder 34 is connected to the sheave wheel 32 and provides an outputsignal to the logging system electronics 36 and provides a signal to adepth monitoring and recording system 38. Logging cable 30 also providesa signal to a logging cable interface device 40. Logging cable interfacedevice 40 is connected to logging system electronics 36 and the boreholeteleviewer data recording system 42.

FIG. 2 is a simplified block diagram of a depth monitoring and recordingsystem for a well logging system. Depth monitoring and recording system38 includes an encoder interface 44 which is connected directly to theoutput of the optical encoder 34. Encoder interface 44 may be connectedto the output of optical encoder 34 using an optical encoder Tconnection 35 which can be a set of pigtails which allows each loggingcompany's unique optical encoder output to be input into encoderinterface 44. Microcontroller 46 is electrically connected to encoderinterface 44 and receives inputs from a count/depth converter 48 whichmay be a set of thumb-wheel switches or a computerized lookup table andreceives input from VCR 50 (e.g., a Panasonic AG-6300). Microcontroller46 provides inputs to VCR 50 and provides outputs to display interface52 and plotter interface 54. VCR 50 provides data input signals todisplay interface 52 nnd plotter interface 54 in the playback modethrough microcontroller 46.

FIG. 3 is a graph showing the time relationship of pulses in anembodiment of the well logging system, it shows a quadrature pulsingsystem signals for up and down counts and is an example of one type ofinput signal which encoder interface 44 is capable of accepting. Butother up-count and down-count signal configurations could also be used.

FIG. 3(a) shows a typical quadrature pulsing system signature for anup-count (increasing depth) situation. Such a signal is generallyproduced by optical encoder 34 and is decoded by looking at the value ofsignal B at the time that signal A is rising. If, for xxample, signal Bis low as is shown in FIG. 3(a) at the time signal A is rising, thensuch a system could consider that configuration to be an up-count.Conversely, in the same system, if signal B were high at the time thatsignal A was rising, the system could consider that situation to be adown-count situation as is shown in FIG. 3(b).

FIG. 4 shows an example of an depth signal interface for a quadraturepulsing system. Signals A and B are provided to depth signal interface56 are provided to input terminals 58 and 60, respectively. Depth signalinterface 56 may include, for example, a retriggerable one-shot,multi-vibrator which transforms quadrature pulsing signals A and B andprovide up-pulses on one output terminal, for example, output terminal62 or down-pulses on a different output terminal, for example, outputterminal 64.

The operation of depth monitoring and recording system 38 for welllogging system 10 can be best understood by once again referring toFIG. 1. Logging cable 30, which is attached to ultrasonic loggingapparatus 14 passes sheave wheel 32, which, since it has a fixedcircumference, scan be used as a measure of the length of cable thatpasses over it by counting the number of rotations or portions thereof.Optical encoder 34 produces pulses corresponding to sheave wheel 32rotations. Optical encoder 34 provides electrical pulses to depthmonitoring and recording system 38. As was described above, the outputfrom optical encoder 34 may be in the form of the quadrature of pulsesas shown in FIG. 3 or some other similar configuration of pulses. Theoptical encoder signals may be buffered with a set of differential linereceivers, which can be used to receive differential or single-endedinputs as is well-known in the art. In addition, encoder interface 44may also include a depth signal interface similar to that shown in FIG.4, for transforming the signal shown in FIG. 3 to a useable input formicrocontroller 46. Microcontroller 46 accumulates counts into a rawdepth number and, as shown in FIG. 2, uses a pulses per foot scalefactor input which is entered from a count/depth converter (for example,thumbwheel switches or a look-up table) to calculate the actual depth.Microcontroller 46 also calculates highly accurate logging speed forpresentation to the operator which may be as accurate as, for example, atenth of a foot per minute. This causes the update of the logging speedto be rather slow at small scale factors but because very accuratemonitoring of logging speed is important, slow updates are tolerated.

As was discussed above, VCR 50 receives inputs from microcontroller 46and from logging cable interface 40. Logging cable interface 40 providesinput to the video channel on the VCR 50 while microcontroller 46provides input to an audio channel of the VCR 50. In addition, a northsynchronizing mark-synchronizing pulse is placed on the VCR 50 audiochannel with the depth information.

FIG. 5 shows the time relationship of an embodiment of an encoded depthsignal 65. The output of microcontroller 46 is an asynchronous serialoutput having a five word frame of information. The technique forencoding the serial bit stream is a frequency burst technique where a"one" is an output of the frequency and a "zero" is no frequency output.Typical VCR 50 audio channel frequency response is 100 hertz to 20,000hertz, direct encoding of the optical encoder 34 output or encoderinterface 44 output would be very difficult because of long periods atthe "zero" level would cause the frequency to be below 100 hertz andcause incorrect decoding.

FIG. 5 shows the time relationship between thenorth-synchronizing/mark-synchronizing pulse 66 and the frame ofinformation 68. As mentioned above, frame of information 68 contains 5cells, 70, 72, 74, 76 and 78. The width of pulse 66 is approximately 100microseconds. The leading edge of frame of information 68 is delay forsome time after the leading edge of pulse 66, for example, 7.5milliseconds.

Each cell of frame 68 is the encoded asynchronized bit stream of acommunications port, for example, an RS-232 port. Encoding of the frameof information may be accomplished using a multiplex frequency which is8 times the baud rate, a harmonic of the baud rate, for example, of thecommunications port. This multiplex frequency is produced during a "one"which is defined by the start bit polarity. Values for a system could be600 baud and 4800 hertz for the multiplex frequency.

The encoded signal 65 amplitude may be between 0 and 2 volts and may beproduced by TTL gate through an attenuation network both of which arewell-known in the art.

The configuration of the cell is two-stop bits, eight-data bits and noparity. Cell 70 is a preamble of alternating "one and zeros". (AA Hex).Cell 72 is the most significant depth byte. Cell 74 is the middle depthbyte and cell 76 is the least significant depth byte. Cell 78 may beused for other purposes, such as a gamma ray value during nuclear welllogging. The depth value input to VCR 50 from microcontroller 46 isnormally raw depth counts not footage.

Referring again to FIG. 2, it is seen that microcontroller 46 alsoprovides depth updates to the plotter interface 54. Microcontroller 46also can provide an output via a standard RS232 port where it is used bya digitizing system (not shown) which correlates depth with the boreholeteleviewer output signal.

When the depth monitoring and recording system 38 is placed in theplayback mode, the microcontroller 46 receives raw depth counts from theVCR 50.

FIG. 6 shows a block diagram for depth decoding for use in a playbackcircuit of VCR 50. Audio information decoder 80 receives an input fromVCR 50 and provides an output to microcontroller 46. The decoding of theaudio information within audio information decoder 80 is accomplished byfirst rejecting all frequencies except the multiplex frequency, forexample, 4800 hertz, in bandpass filter 82. Comparator 84 squares theanalog signal provided by bandpass filter 82 and produces a TTL signalfor input to multi-vibrator 86. Multi-vibrator 86 is set to a pulsewidth slightly greater than the period of the multiplex frequency (forexample, 4800 hertz). Multi-vibrator 86 output is the asynchronousserial input to microcontroller 46 during playback which thereby enablesmicrocontroller 46 to read the information, display depth, and outputinformation through another serial port to a digitizing computer as wellas calculating a logging speed. A digitizing computer (not shown) canreceive televiewer amplitude and travel time through another interfaceand correlate the received information with televiewer depth.

Recording of televiewer data is, in some instances accomplished byrecording the analog signal from the borehole televiewer on a VCR 50.Some modifications are necessary particularly defeating of the AGCfeature and proper vertical synchronization. The AGC must be defeated sothat true analog signals may be recorded allowing accurate reproductionof acoustic amplitudes. Vertical synchronization is needed in order toset the VCR motor speed for accurate playback of the borehole televieweranalog signal.

Referring once again to FIG. 2, there is shown a borehole televiewerdata recording system interface 42 which provides the analog acousticsignal developed by the ultrasonic logging apparatus 14 and transmittedalong logging cable 30 through logging cable interface 40. Boreholeteleviewer data recording system interface 42 provides the analogacoustic signal to VCR 50.

As was mentioned above, in order to provide an accurate representationof acoustic amplitude of the received signal, the AGC circuitry of theVCR 50 must be defeated.

FIG. 7 shows the time relationships of an input signal for a boreholeteleviewer and a corresponding AGC adjusting signal. In particular, FIG.7 shows a synchronization pulse 88 and an acoustic return pulse 90 whichwould be typical of the pulses received by VCR 50 from boreholeteleviewer recording system interface 42. Signal A is then levelshifted, inverted and multiplexed with ground while being superimposedover the sync pulse of the televiewer signal as shown in FIG. 7, SignalB. The synchronization signal 88 is an input from the boreholeteleviewer system logging cable interface 40.

In order to accomplish the defeating of the AGC a minor modification toVCR 50 is required. Extra capacitance is added to the AGCsynchronization detect circuitry to allow extra time between AGC pulseswhich is well-known in the art.

FIG. 8 shows the time relationship of a received synchronizing pulse andacoustic return signal. The interaction of the generated acousticwaveform 92 and the borehole produces an acoustic return 94 as in FIG.8(a). FIG. 8(a) while depicting the amplitude of acoustic return 94, isnot shown to scale with respect to the amplitude of the generatedacoustic waveform 92. The acoustic return 94 includes a reflectionportion 96 which is caused by the reflection of the generated acousticwaveform 92 off of the inner surface 22 of the casing wall. The acousticreturn 94 is received by ultrasonic logging apparatus I4.

The acoustic return 94 has two measured parameters, time of travel andamplitude, which give an indication of the condition of the investigatedsurface. Referring to FIG. 8(a), the time of travel T_(t) is the timebetween the initiation of the generated acoustic waveform 92 and thedetection of acoustic return 94. The time of travel T_(t) gives ameasurement of twice the distance of the investigated inner surface 22from the transducer contained in the ultrasonic logging apparatus 14.The amplitude is the peak amplitude of acoustic return 94 and it givesan indication of the type of surface being investigated. In general, anyirregularities on the investigated surface will reduce the amplitude ofthe acoustic return.

FIG. 8(b) shows the application of the present invention to anothermethod of transmitting the analog acoustic signal. In FIG. 8(b) thewaveform in FIG. 8(a) has been transformed into a synchronizing pulse 98followed by a waveform envelope whose peak amplitude 102 corresponds tothe peak amplitude of acoustic return 94 and where the time of travel Tis represented by the time between the synchronizing pulse 98 which issynchronized with the transmitted acoustic waveform 92 and leadingdetectable edge of acoustic return envelope 100. AGC defeating pulse 104is shown superimposed on synchronizing pulse 98.

In another useful embodiment as is shown in FIG. 8(c), AGC defeatingpulse 104 is superimposed on synchronizing pulse 98. The time of travelT_(t) is measured between the leading edge of synchronizing pulse 98 andthe leading edge of time of travel pulse 106. Amplitude information inthis embodiment is provided by referring to amplitude pulse 108.

FIG. 9 shows the time relationships a modified synchronizing signal witha superimposed AGC control signal and a bipolar acoustic signal 97.Again, in FIG. 9, the AGC defeating pulse 104 is superimposed oversynchronizing pulse 98 which is followed by time of travel pulse 106 andamplitude pulse 108.

FIG. 10 shows the time relationship of the synchronizing signal and themodified acoustic signal 97 of FIG. 9 transformed into a time of traveland an amplitude signal. In another useful embodiment, AGC defeatingpulse is superimposed on synchronizing pulse 98 followed by time oftravel pulse 106 and amplitude pulse 108. Also included in this acousticreturn information is an expanded acoustic waveform 110 whichcorresponds to the waveform received by ultrasonic logging apparatus 14.

FIG. 11 shows a bipolar version of the signal in FIG. 10 with itsassociate AGC control pulse. For purposes of illustration, FIG. 11 showsa signal similar to that shown in FIG. 10 but any borehole televiewerdata signal could be used. Synchronizing pulse 98 is, in actuality, thehorizontal synchronizing pulse input to the VCR 50. Acoustic informationsignal 111 is shown along with vertical synchronization signal 112.

Vertical synchronization for VCR 50 is provided using an externalsynchronization input as is well known in the art. This externalsynchronization input can be derived either from an internal (forexample, 60 hertz) oscillator or from the ultrasonic logging apparatus14 synchronizing pulse 98 whose frequency of, for example, 1500 hertzcan be divided by 25 to yield, for example, a 60 hertz verticalsynchronizing signal 112.

VCR 50 may require that a vertical synchronization signal 112 have anaccuracy of plus or minus 1 hertz. This requires ultrasonic loggingapparatus 14 which produce a horizontal synchronizing pulse 98 ofaccurate and stable frequency.

VCR 50, as is common in the prior art, has a two-head recording systemwhich switches between the head at the 60 hertz system synchronizingfrequency. When switching between recording heads, there may be adiscontinuity in the recording. The borehole televiewer system has acontinuous stream of acoustic return information 111. Therefore,acoustic return information 111 could be degraded by this switchingglitch.

In one useful embodiment of the invention, synchronizing pulse 98 isused to generate vertical synchronization signal 112. If, for example,synchronizing pulse 98 is a 1500 hertz signal, it is divided by 25 andproduces an output 60 hertz vertical synchronizing signal 112substantially in phase with the synchronizing pulse 98. The leading edge114 of vertical synchronizing signal 112 can be shifted by a time T_(d)using techniques well known in the art. T_(d) is optimally selected toplace leading edge 114 of vertical synchronizing signal 112 at aposition with respect to acoustic information signal 111 wherein no datais being transmitted. Thus, any discontinuity which may occur due to theshifting from one recording head of VCR 50 to another will occur duringa period when no data is being transmitted and, therefore, nodegradation of acoustic returned information will occur.

Although the method of the present invention has been described inrelation to a cased borehole, the method can also be used with acousticreturns obtained from an open borehole.

Although several embodiments have been described in detail, it should beunderstood that various changes, substitutions and alterations can bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. A depth system for measuring and recording thedepth of a well logging tool comprising:a) a depth signal interface forproducing a first plurality of pulses corresponding to changes in thedepth of the well logging tool; b) a microcontroller electricallyconnected to said depth signal interface for transforming said firstplurality of electrical pulses to a digital serial bit stream using afrequency burst technique wherein the frequency of a burst is in theaudio frequency range, and for developing a digital well logging speedsignal; c) logging cable interface device electrically connected to thewell logging tool for transmitting data from the well logging tool and asynchronizing pulse; d) an analog vido recording device electricallyconnected to said microcontroller and said logging cable interfacedevice for recording said digital serial bit stream a predetermined timeafter said synchronizing pulse on a single audio channel of the analogvideo recording device; and e) a display interface in electricalcommunication with the microcontroller for generating a video displaysignal said video display including the well logging speed signal. 2.The system of claim 1 wherein said audo frequency source has a frequencyof between 100 and 20,000 Hz.
 3. The system of claim 1 wherein saidaudio frequency source has a frequency of 4800 Hz.
 4. The system ofclaim 1 wherein said encoder has an output data rate of 600 Baud.
 5. Thesystem of claim 1 wherein said recording device has a playback circuitand a recording circuit.
 6. The system of claim wherein saidmicrocontroller has a serial output for computer.
 7. The system of claim1 wherein said microcontroller produces a five word frame correspondingto the depth of the well logging tool.
 8. A depth system for measuringand recording the depth of a well logging tool comprising:a) a depthsignal interface for producing a first plurality of pulses correspondingto changes in depth of the well logging tool; b) a microcontrollerelectrically connected to said depth signal interface for transformingsaid first plurality of electrical pulses to a digital serial bit streamusing a frequency burst technique wherein the frequency of a burst is inthe audo frequency range; c) logging cable interface device electricallyconnected to the well loggin gtool for transmitting data fro the welllogging tool and a synchronizing pulse; and d) an analog video recordingdevice electrically connected to said microcontroller and said loggingcable interface device for recording said digital serial bit stream apredeterined time after said synchronizing pulse on a single audiochannel of the analog video recording device.